Van der Waals and Nonbonded Radii of Atoms

In a molecule of chlorine, with the electronic structure Cl Cl , the covalent radius of chlorine may be described as representing roughly 

The van der Waals radius is expected to be larger than the covalent radius, since it involves the interposition of two electron pairs between the atoms rather than one. Moreover, the van der Waals radius of chlorine should be about equal to its ionic radius, inasmuch as the bonded atom presents the same face to the outside world in directions 

18 These are mainly the London dispersion forces, the nature of which we shall not discuss. See F. London, Z. Phyeik 63, 245 (1930) Also Introduction to Quantum Mechanics. 

The ionic radius of chlorine has the value 1.81 A (Chap. 13). The following distances between chlorine atoms of different molecules have been observed in the molecular crystal 1,2,3,4,5,(Whexachlorocyclo-hexane.-57 3,60, 3.77, 3.82 A these are close to twice the ionic radius. Similar agreement is shown by many other organic crystals and inorganic covalent crystals. Cadmium chloride, for example, consists of 

Other nonmetallic elements also are found to have van der Waals radii approximately equal to their ionic radii. For sulfur, for example, in the layer crystal molybdenite, the van der Waals radius effective be- 

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These van der Waals radii are only distantly related to the constant b in the van der Waals equation of state (p+ajv ) (V-b)=RT, and the great Dutch chemist would undoubtedly have been surprised to know that his name was to be associated with them. Indeed, it is difficult to trace how the term established itself in the everyday language of structural chemistry. One likely source is Pauling s influential text The Nature of the Chemical Bond. In the section entitled Van der Waals and Nonbonded Radii of Atoms , Pauling wrote ... 

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